fix: only make fetch_from field read only if no input (#19192) (#19195)

(cherry picked from commit 7578be8)

Co-authored-by: Ankush Menat <ankush@frappe.io>

frappe/public/js/frappe/form/controls/base_input.js

@@ -52,6 +52,14 @@ frappe.ui.form.ControlInput = class ControlInput extends frappe.ui.form.Control
 		}
 	}
 
+	read_only_because_of_fetch_from() {
+		return (
+			this.df.fetch_from &&
+			!this.df.fetch_if_empty &&
+			this.frm?.doc?.[this.df.fetch_from.split(".")[0]]
+		);
+	}
+
 	// update input value, label, description
 	// display (show/hide/read-only),
 	// mandatory style on refresh
@@ -82,7 +90,7 @@ frappe.ui.form.ControlInput = class ControlInput extends frappe.ui.form.Control
 				me.value = me.doc[me.df.fieldname] || "";
 			}
 
-			let is_fetch_from_read_only = me.df.fetch_from && !me.df.fetch_if_empty;
+			let is_fetch_from_read_only = me.read_only_because_of_fetch_from();
 
 			if (me.can_write() && !is_fetch_from_read_only) {
 				me.disp_area && $(me.disp_area).toggle(false);